Re: Wow...so intriguing...
I'd also mention that vacuum is much, much thinner than helium, so if you can't make something that can keep helium in, you certainly can't keep a vacuum in. Also as soon as you put anything consumer grade in a vacuum, almost everything outgasses, meaning you end up with no vacuum.
I suppose that they could always fit a turbomolecular pump to every drive, but it might cancel out the capacity density improvements .